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async fn in trait should require async fn in impl #102745

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compiler-errors opened this issue Oct 6, 2022 · 6 comments · Fixed by #104592
Closed

async fn in trait should require async fn in impl #102745

compiler-errors opened this issue Oct 6, 2022 · 6 comments · Fixed by #104592
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@ComputerDruid
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F-async_fn_in_trait Static async fn in traits

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@compiler-errors
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compiler-errors commented Oct 6, 2022 •
edited by rustbot
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For now, we've decided that an async fn() -> T in a trait should not be satisfied by a fn() -> Type where Type: Future<Output = T> until we at least hammer out how #[refine] is gonna work, etc.

So let's just do a HIR check that the signatures are compatible.
@compiler-errors
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Assigning to @ComputerDruid who expressed interest in working on this.

@compiler-errors
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@rustbot assign @ComputerDruid

idk if that works, the github UI doesn't let me assign to you 😝

@rustbot rustbot self-assigned this Oct 6, 2022
@compiler-errors
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ugh lol

@compiler-errors compiler-errors added the F-async_fn_in_trait Static async fn in traits label Oct 6, 2022
@ComputerDruid
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@rustbot claim

@rustbot rustbot assigned ComputerDruid and unassigned rustbot Oct 6, 2022
@zirconium-n
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Should it be satisfied with fn() -> impl Future<Output = T> ?

@compiler-errors
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I think not for now, and certainly not without the user enabling the return_position_impl_trait_in_trait feature gate

@compiler-errors compiler-errors mentioned this issue Oct 27, 2022
Merged
matthiaskrgr pushed a commit to matthiaskrgr/rust that referenced this issue Oct 28, 2022
@bryangarza
Update tests based on feedback
bfdefdb 
- Add comment to some tests that will break when rust-lang#102745 is implemented
- Mark a test with known-bug
- Delete duplicate test
@ComputerDruid ComputerDruid mentioned this issue Nov 19, 2022
Merged
ComputerDruid added a commit to ComputerDruid/rust that referenced this issue Dec 9, 2022
@ComputerDruid
Ensure async trait impls are async (or otherwise return an opaque type)
259c37e 
As a workaround for the full `#[refine]` semantics not being implemented
yet, forbit returning a concrete future type like `Box<dyn Future>` or a
manually implemented Future.

`-> impl Future` is still permitted; while that can also cause
accidental refinement, that's behind a different feature gate
(`return_position_impl_trait_in_trait`) and that problem exists
regardless of whether the trait method is async, so will have to be
solved more generally.

Fixes rust-lang#102745
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Dec 14, 2022
@matthiaskrgr
Rollup merge of rust-lang#104592 - ComputerDruid:async_check, r=compi…
79653c8 
…ler-errors

Ensure async trait impls are async (or otherwise return an opaque type)

As a workaround for the full `#[refine]` semantics not being implemented
yet, forbit returning a concrete future type like `Box<dyn Future>` or a
manually implemented Future.

`-> impl Future` is still permitted; while that can also cause
accidental refinement, that's behind a different feature gate
(`return_position_impl_trait_in_trait`) and that problem exists
regardless of whether the trait method is async, so will have to be
solved more generally.

Fixes rust-lang#102745
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Dec 15, 2022
@matthiaskrgr
Rollup merge of rust-lang#104592 - ComputerDruid:async_check, r=compi…
60913c2 
…ler-errors

Ensure async trait impls are async (or otherwise return an opaque type)

As a workaround for the full `#[refine]` semantics not being implemented
yet, forbit returning a concrete future type like `Box<dyn Future>` or a
manually implemented Future.

`-> impl Future` is still permitted; while that can also cause
accidental refinement, that's behind a different feature gate
(`return_position_impl_trait_in_trait`) and that problem exists
regardless of whether the trait method is async, so will have to be
solved more generally.

Fixes rust-lang#102745
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Dec 15, 2022
@matthiaskrgr
Rollup merge of rust-lang#104592 - ComputerDruid:async_check, r=compi…
7c9c03a 
…ler-errors

Ensure async trait impls are async (or otherwise return an opaque type)

As a workaround for the full `#[refine]` semantics not being implemented
yet, forbit returning a concrete future type like `Box<dyn Future>` or a
manually implemented Future.

`-> impl Future` is still permitted; while that can also cause
accidental refinement, that's behind a different feature gate
(`return_position_impl_trait_in_trait`) and that problem exists
regardless of whether the trait method is async, so will have to be
solved more generally.

Fixes rust-lang#102745
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Dec 15, 2022
@matthiaskrgr
Rollup merge of rust-lang#104592 - ComputerDruid:async_check, r=compi…
c00eac3 
…ler-errors

Ensure async trait impls are async (or otherwise return an opaque type)

As a workaround for the full `#[refine]` semantics not being implemented
yet, forbit returning a concrete future type like `Box<dyn Future>` or a
manually implemented Future.

`-> impl Future` is still permitted; while that can also cause
accidental refinement, that's behind a different feature gate
(`return_position_impl_trait_in_trait`) and that problem exists
regardless of whether the trait method is async, so will have to be
solved more generally.

Fixes rust-lang#102745
@bors bors closed this as completed in da98ef9 Dec 15, 2022
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Ensure async trait impls are async (or otherwise return an opaque type) ComputerDruid/rust
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